1. Field of the Invention
The present invention relates generally to optical disc apparatuses for recording information on or reproducing recorded information from an optical disc. More particularly, the invention concerns a method for controlling a beam expander within an optical pickup.
2. Description of the Related Art
In Blu-ray discs (BDs) with a high-density recording capacity, since a first recording layer and a second recording layer are disposed at desired intervals in the perpendicular direction of the disc, spherical aberration occurs when control is switched from one of the recording layers to the other. In order to correct the spherical aberration, optical disc apparatuses contain a motor-driven correcting lens assembly called a beam expander, in respective optical pickups. The beam expander comprising a fixed lens and a movable lens corrects the spherical aberration by moving the movable lens while controlling the position thereof with a stepping motor. The stepping motor, when driven, will naturally give off heat and thus increase the ambient temperature of the motor. The ambient temperature, in particular, needs to be limited below its maximum permissible level to minimize effects upon the operational performance of the optical pickup.
To suppress the emanation of heat from the stepping motor during the activation of the beam expander, it is effective to reduce the driving current or driving time of the motor. A technique for controlling aberrational correction according to ambient temperature in order to stabilize the operation of a beam expander against temperature changes is proposed as an alternative method (refer to JP-A-2006-185498).